Bards provide unparalleled melee damage buffs. A level 14 Warchanter can give the entire party an undispellable +9/+8 attack/damage buff. That's pretty freaking huge in a melee-heavy group (like the first one matt listed).
Bards also have Fascinate, which while certainly situational, is also unsaveable CC. And obviously there are Haste and Displacement buffs; I find Bards are good to have around to hand out those buffs, even if I already have a Sorcerer present. It frees up quite a bit of mana for the Sorcerer to blast.
If built for a melee bias, Bards can also put out some pretty sick DPS, too. They'll never compete with dedicated melee builds who also have the Bard's buffs, but then again, that's sort of the point.
As to the three Clerics, I have no idea. Clerics can do some very serviceable offensive casting though, and they can sub in for meleers in a pinch. Caster-heavy groups become more and more effective as the levels rise, but that's not unexpected to anyone who's played DnD.
Yes, that does seem rather odd.edit: Did anyone else find it funny that he objects to using raid items in planning out a build, but thinks using multiple mana pots a quest is everyday play?